Monday, January 12, 2009

Air Receivers

Air Receivers

Every compressed air system needs a receiver, but the receiver alone is not always the answer to energy efficiency in the system.With its dumpy fat cylindrical shape, dull-painted exterior, lack of visible dynamic activity, and frequently hidden location, it's easy to understand why the air receiver usually is the orphan of the plant-air system family. There is confusion and controversy over its function, where it should be located, what size it should be, how it should be piped - and whether an air receiver is needed at all.Air receivers are one of the least understood, yet potentially most useful components available to increase operating efficiency.

But an air receiver should be an integral part of any plant air system - mainly to enhance its efficiency.

Here are the classic purposes:

Contaminant removal - A bare receiver (without a pressure regulator or flow controller) adds a large volume to the piping system. This volume reduces air-flow velocity and encourages finely divided particles of liquid lubricant or condensate to drop out of the air stream. These separated liquids then can be drained from the receiver, rather than traveling with the compressed air to produce adverse downstream effects.

Pulsation dampening - A receiver installed near the compressor discharge dampens pressure pulses from positive-displacement compressors (rotary or reciprocating) to a small fraction of their original amplitude. This reduces the probability of excess compressor power or shortened service life resulting from rapid recycling of the compressor.

Pressure stabilization - A receiver combined with a pressure regulator or flow controller can create an effective pressure band or differential between the supply side and the demand side. A typical example: 95 psig in the receiver, 90 psig steady to the system. This will allow the demand side to operate at its lowest effective pressure, and therefore lowest volume demand. Stored air with a pressure differential creates volume held in reserve to cover short-term peak demands that exceed current air supply.

Controlling energy costsWhen industry management began to focus on energy-cost control as a weapon for reducing production costs, energy managers soon realized that compressed air was their most expensive utility. After all, it takes 8 hp of electricity to produce 1 hp of compressed air. Air no longer was perceived as free. Its cost should, and could, be managed.

Early efforts in compressed-air cost management focused on the obvious - control of leaks and lowering usage.

Without effective storage, most unloading controls could not establish and hold enough idle time as a percent of running time. Nor could they optimize the automatic start/stop control and shut off.